Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-11-10
2003-07-15
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395430
Reexamination Certificate
active
06594265
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to Asynchronous Transfer Mode (ATM) networks, and more particularly to a method and system for providing an Available Bit Rate (ABR) interface to a non ATM bandwidth adjustable Virtual Path Connection (CBR VPC).
BACKGROUND ART
High Speed Communication Networks
In modern telecommunication networks, different types of applications must share the same transmission media, and networks equipment must be able to support these different services while guaranteeing to each of them a specified quality of service. While some years ago, voice and data used separate networks, they now share bandwidth of the same links. For the last three years, standards organizations have worked to define transmission modes, such as ATM (Asynchronous Transmission Mode), Frame Relay, and so forth, and inside a particular transmission mode, to specify in detail the services provided to network applications. For ATM, for instance, four different service categories exist, and a user will choose one of them based on the type of service required:
Continuous Bit Rate (CBR)
This service is intended for uncompressed voice, and highest priority applications (video). The cost of this service is the highest because the bandwidth which is reserved corresponds to the maximum rate (Peak Cell Rate PCR) at which this type of application can emit. This is the bandwidth to allocate when the quality of service, in terms of maximum Cell Transfer Delay (maxCTD) and Peak to peak Cell Delay Variation (peak to peak CDV), must be guaranteed whatever the network load conditions.
Variable Bit Rate (VBR)
This service is a compromise between the Continuous Bit Rate (CBR), which requires a lot of resources, and a service where no reservation of bandwidth would be done. Effectively here, a bandwidth comprised between the Sustainable Cell Rate (SCR) of the connection and the Peak Cell Rate (PCR) of the connection is allocated, depending on the burstiness of the traffic. When the bursts created by the application in the network are limited, a bandwidth close to the Sustainable Cell Rate (SCR) is reserved. When the bursts induced by the application are large (or may be large), a bandwidth closer to the Peak Cell Rate is reserved to avoid overloading links and buffers, and loss of data.
While the service offered here also guarantees a very low loss of packets or cells (Cell Loss Ratio CLR), the transfer delays and cell delay variations are more important than for CBR. In general, VBR can be divided into VBR Real Time (good candidate for video and data RT applications) and VBR Non Real Time (good candidate for data sensitive traffic).
Unspecified Bit Rate (UBR)
This service is totally uncontrolled. Traffic is sent in the network, and is transmitted provided that the network is not congested. When the network is congested, cells are discarded. Unlike CBR and VBR, no quality of service can be guaranteed.
Available Bit Rate (ABR)
This service provides again less quality than Variable Bit Rate (VBR), and can be used for different applications. While a minimum reservation can be done in the network to guarantee to an application a “worst case” behavior, the steady state behavior of the service offered corresponds to a “non reserved” type of service, where nearly no resource is allocated in the network. When congestion occurs, feedback is conveyed through the network back to the traffic sources to prevent them from sending more data. This reactive system behavior is directly linked to the network size. The delay to convey back congestion information to the sources increases as a function of the network size, and may nevertheless induce losses. In this case, end users make decisions to send the data again. Here neither the delays nor the losses can be guaranteed; the service is only assumed to minimize the losses.
All these different services are proposed and used simultaneously in most networks.
Bandwidth Optimization
Most wide-area ATM networks (large country, world-wide networks) are configured so that an ATM backbone network can support communications between different ATM access networks. Such network topology allows good performance and the optimization of the network administration. Generally, the backbone network is a public ATM network, and access networks are private ATM networks. However, the backbone can be used within a single private network using, for example, lines leased from a carrier. To optimize the resources where they are most demanded, in particular the bandwidth within the backbone network, several solutions can be implemented, all taking into account the dynamic availability of the bandwidth:
1. End to End Available Bit Rate Virtual Channel Connections (ABR VCCs) for Data Traffic
This solution, as illustrated in
FIG. 5
, supposes the support of ABR VCCs by all end-systems (source node
1
and destination node
8
). The advantage is that intermediate nodes within access networks and within the backbone network (nodes
2
to
7
) have only to set an Explicit Forward Congestion Indication (EFCI) bit in the ATM cells to be compliant with the ATM Forum recommendation (ATM Forum—Technical Committee—“Traffic Management Specification,” version 4.0, April 96, paragraph 5.10.6, rule 1.a)). End-systems (nodes
1
and
8
) connected to users (user
1
and user
2
) do the most complex process, in particular:
the ABR source behavior (node
1
) including:
generation of Resource Management cells (RM-cells),
insertion of RM-cells in the traffic,
computation of a transmission rate per VCC based on congestion information received from RM-cells,
dynamic traffic shaping, and
the ABR destination (node
8
) behavior including:
transmission of RM-cells back to the source in response to forward RM-cells,
setting of the congestion fields within RM-cells, and
insertion of RM-cells in the traffic.
A more sophisticated implementation of the Available Bit Rate (ABR) category of service in intermediate nodes is described in the ATM Forum paragraph 5.10.6, rule 1.c). The so called “switch behavior” allows the control of congestion at queuing points, and in particular the modification of the Explicit Rate (ER) field within RM-cells for a better response to congestion and thus a lower cell loss.
2. Available Bit Rate Virtual Path Connections (ABR VPCs) in the Backbone
FIG. 6
is a view of a network comprising a first access network (access network
1
) comprising an end node (node
1
) connected to a user (user
1
) and a source node (source node
2
), a backbone network comprising a plurality of nodes (node
3
, node
4
, and node
9
) and a second access network (access network
2
) comprising a destination node (destination node
5
), transit nodes (nodes
6
and
7
), and an end node (node
8
) connected to a user
2
. An ABR VCC is established between nodes
2
-
5
, to transmit, to node
5
, traffic of end user
1
(VCC
1
) together with traffic of other end users (VCC
3
). In node
5
, traffic is discriminated according to its destination, and transmitted to end user
2
(VCC
2
) and to other end users (VCC
4
).
ABR Virtual Path Connections (VPCs), as illustrated in
FIG. 6
, are set up in the backbone network for interconnecting access networks (access networks
1
and
2
). The nodes within the access networks directly connected to the backbone network (nodes
2
and
5
) use these ABR VPCs to transport VCCs (VCC
1
, VCC
3
). In order to comply with the ATM Forum recommendations (paragraph 5.10.9), these nodes implement the ABR source and destination behavior as described in paragraphs 5.10.4 to 5.10.9. Access nodes (nodes
2
and
5
) must also be able to provide a fair share of the bandwidth of these Virtual Path Connections (VPCs) among the different Virtual Channel Connections (VCC
1
, VCC
3
) they support.
3. Continuous Bit Rate Virtual Path Connections (CBR VPCs) with Adjustable Bandwidth in the Backbone
FIG. 7
is a view of a network comprising a first access network (access network
1
) comprising an end node (node
1
) connected to a user
1
and a source node (source node
Etorre Yves Nicolas
Fichou Aline
Galand Claude
Chin Wellington
Fox Jamal
Irvin David R.
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